The present invention relates to a magnetic head, for forming guard bands on a magnetic recording medium, and a process of fabrication thereof and, more particularly, to a magnetic head suitable for use in a recording and reproduction device for magnetic discs.
In a magnetic disc device for forming recording tracks in the circumferential direction around a disc-shaped recording medium, crosstalk between adjacent tracks becomes a problem during reproduction if the spacing of the tracks is reduced to increase the recording density.
For this purpose, the recording and reproduction magnetic head used in the prior art has a structure such as that shown in FIGS. 1 and 2. This magnetic head is constructed of three head cores 10, 11 and 12. The first head core 10 is formed so that it has a functional gap 14 and a coil-winding aperture 15, and is constructed of a magnetic core portion 13 made of ferrite and an L-shaped member 16 made of a non-magnetic material such as ceramic. Similarly, the second and third head cores 11 and 12 are constructed of magnetic core portions 17 and 18 of ferrite and L-shaped non-magnetic members 23 and 24, respectively, and are formed so as to have functional gaps 19 and 20 and coil-winding apertures 21 and 22, respectively. The head cores 10, 11 and 12 are cut to predetermined widths out of the same block and are joined together to form a monolithic structure, as shown in FIG. 2. The central head core 10 is used for recording and reproduction, whereas the head cores 11 and 12 at either side thereof are used for erasure.
Because of this construction, the pair of erasure gaps 19 and 20 scan only the side portions of the recording track formed by the recording and reproduction gap 14 on the surface of the recording medium adjacent to the magnetic head of FIG. 2. As a result, the two sides of the recording track act as guard bands which are substantially completely signalless, so that little crosstalk is generated from adjacent tracks during the reproduction, even if the track spacing is narrowed.
In the magnetic head of this construction, however, the head cores 10, 11 and 12 have to be connected together after being cut from the block. During this process, the alignment of each of the gaps 14, 19 and 20 in particular is an extremely difficult job. If the track width is 30 .mu.m or less, moreover, the mechanical strength of the head cores is reduced so that they are difficult to machine.
Recently in order to reduce the recording wavelengths used, a recording medium utilizing high coercive forces has been employed. As a result, conventional magnetic heads made of a ferrite material are not capable of adequately recording on such a recording medium. Magnetic materials with high saturation magnetic flux densities and high permeabilities are limited to metallic magnetic materials. As known in the art, however, the metallic magnetic materials in bulk have the disadvantage that they cannot provide satisfactory characteristics in the high-frequency range because of eddy-current losses. In order to avoid this disadvantage, a magnetic head has been proposed which employs multi-layered metallic magnetic films prepared by thin-film formation techniques. It is, however, extremely difficult to realize the magnetic head of the structure of FIGS. 1 and 2 by this method.
Japanese Patent Laid-Open No. 57-44219 a magnetic head in which a head element portion, having a recording and reproduction gap, and a head element portion, having a pair of erasure gaps are joined together such that they are arranged to have their individual gaps in parallel with each other and such that they are perpendicular to the gap direction. However, the magnetic head thus disclosed does not use a thin film of metallic magnetic materials so that it cannot obtain the advantage which could be obtained by making the magnetic materials thin.
The present invention is designed to solve these various problems, and provides both a magnetic head which has a recording and reproduction gap and a pair of erasure gaps, and which is remarkably easy to fabricate and is very accurate, and also a process of fabricating such a head. The present invention is also designed to provide both a magnetic head which is so constructed that it can record on a recording medium which utilizes high coercive forces, and can easily form track widths of 20 .mu.m or less, and a process of fabricating such head.
In order to achieve these objects, a magnetic head according to the present invention is of an integrated structure comprising a recording and reproduction head provided with a first core which has a magnetic circuit constructed of magnetic materials formed on a non-magnetic member, and an erasure head provided with second and third cores which have magnetic circuits constructed of magnetic materials formed on another non-magnetic member and which are arranged to erase both side portions of a track width of a magnetically-recorded portion formed on a magnetic recording medium by the recording and reproduction head, by the use of the second and third cores, to leave a desired recording track width, wherein the recording and reproduction head and the erasure head are connected together in the direction in which the magnetic recording medium runs, to provide the integrated structure.
More specifically, the recording and reproduction head is constructed such that ridges of a pair of metallic magnetic films of a generally V-shaped cross-sectional shape which form a magnetic circuit abut against each other from either side of a non-magnetic gap material to form the first core, V-shaped cross-sectional portions thereof are exposed on the surface of the first core facing the magnetic recording medium, flat surfaces are provided on leading edges of the ridges of the pair of metallic magnetic films so as to extend parallel to each other and perpendicular to the direction in which the magnetic recording medium runs, the width of the flat surfaces which is defined by the intersections between those flat surfaces and the surface facing the magnetic recording medium corresponds to the track width, and the metallic magnetic films are formed on the non-magnetic member in which are formed ridges shaped to correspond to the V-shape. The erasure head is constructed such that pairs of V-shaped metallic magnetic films forming magnetic circuits are formed on both surfaces of two non-magnetic members of a V-shaped section so that leading edges of ridges thereof are flat, and the pairs of V-shaped metallic magnetic films are made to abut against each other on either side of a non-magnetic gap material at portions thereof adjacent to the flat surfaces of the leading edges of the magnetic members to form the second and third cores, sections of the metallic magnetic films on both side of the V-shaped portions are exposed on the surface of the second and third cores facing the magnetic recording medium, the abutting portions of each of these pairs of metallic magnetic films extend parallel to each other and generally perpendicular to the direction in which the magnetic recording medium runs, and the width of the flat surfaces which form the leading edges of the non-magnetic members sandwiched between the second and third cores is defined by the intersections between those flat surfaces and surface of the second and third cores facing the magnetic recording medium and is equal to or less than the track width. A typical magnetic head of the present invention can be fabricated by connecting together the recording and reproduction head and the erasure head thus prepared in series in the direction in which the magnetic recording medium runs, to form a monolithic structure, and by equipping this integrated structure with a coil.
The magnetic head of the present invention can be easily fabricated by a process comprising a step (i) of forming at least one coil-winding groove in a side surface of each of two non-magnetic blocks which will form a gap, a step (ii) of forming parallel grooves in the gap-forming side surface of the non-magnetic blocks at right angles to the coil-winding grooves in such a manner that a plurality of ridges are left, a step (iii) of coating at least the grooves of the gap-forming side surface of the non-magnetic blocks with a metallic material after step (ii), a step (iv) of filling the grooves whose surfaces have been coated with the metallic magnetic material with a non-magnetic material, a step (v) of removing unwanted portions of the non-magnetic filler and magnetic material of one of the non-magnetic blocks to expose the gap-forming side surface so that a desired track width is provided, a step (iv) of removing unwanted portions of the non-magnetic filler and magnetic material of the other of the non-magnetic blocks after step (iii) to expose the gap-forming side surface which is provided with both a desired non-magnetic portion and a pair of metallic magnetic members at either side thereof, a step (vii) of cutting the blocks after steps (v) and (vi) at central portions thereof into pairs of core blocks, a step (viii) of forming a non-magnetic layer of a desired thickness on the gap-forming side surface of at least one of the pairs of blocks after step (vii), a step (ix) of connecting in a face-to-face relationship the gap-forming side surfaces of the pairs of blocks after step (viii), a step (x) of connecting together two sets of connected blocks at a predetermined position to form a monolithic structure, and a step (xi) of cutting the thus-connected blocks at a predetermined position to fabricate at least one magnetic head core.
In the present invention, as described above, the first core is constructed by butt-jointing generally V-shaped metallic magnetic members which are formed on the ridges of adjacent non-magnetic protective members, through a non-magnetic gap member. The track width can be regulated by the leading edges of the V-shaped metallic magnetic films to a desired width by polishing the adjacent faces thereof. In this case, a suitable selection can be made within a range such that the ridges of the non-magnetic protective member do not appear. Thus, the first head core provides a recording and reproduction magnetic head.
Next, the second and third head cores are prepared by a method similar to that of the first head core, and are separated into the second and third cores by polishing their gap-forming surfaces during the polishing step until the ridges of the non-magnetic protective members appear. The desired recording track width can be regulated by making the width by which the ridges of the non-magnetic protective members are exposed equal to or less than the track width of the first head core. Specifically, the erasure magnetic head of the second and third cores is formed on either side of the exposed portions of the non-magnetic protective members, so that only the two sides of the recording track recorded by the first head core are scanned by a pair of erasure heads. As a result, both sides of the recording track are provided with guard bands which are substantially completely signalless. The thickness of the coating of the metallic magnetic films is substantially equal to the width of the guard bands, so that the guard band width can be selected as required by changing the thickness of the metallic magnetic films. As a result, the guard bands can be made narrower than those of the prior art of FIGS. 1 and 2.
The first recording and playback head core and the second and third erasure magnetic heads of the above construction are connected in series to form a monolithic structure which provides a single magnetic head.
Thus, according to the present invention, the track width can be regulated as required by changing the thickness of the metallic magnetic films so that it can be easily made less than that of the magnetic head made of a bulk material in accordance with the prior art, and can find a suitable application as a magnetic head for high-density recording. It is also easy to reduce the guard band width.
The metallic magnetic material used in the first core in the present invention can easily be made the same as or different from that of the second and third cores.
In the magnetic head structure of the present invention, it is recommended that a non-magnetic protective material is applied after the coating with the metallic magnetic films, to protect the metallic magnetic films in the vicinity of the gap. The protective material may be filled in with glass or a wear-resistant material such as Al.sub.2 O.sub.3 or SiO.sub.2 may be formed over it, or it may have a structure consisting of two or more layers of this wear-resistant protective material and glass. In this case, the glass can be used as a connecting material for joining together the two core halves.
The metallic magnetic films of the magnetic head core of the present invention may be made of any highly permeable material, so long as it has a higher saturation magnetic flux density Bs than that of the conventional ferrite and a magnetic distortion in the vicinity of zero, and may be either a polycrystalline metallic magnetic material, which is represented by the Fe--Al--Si alloys (or the so-called "Sendust alloys"), or the Ni--Fe alloys (or the so-called "Permalloy alloys"), or an amorphous magnetic alloy material. These magnetic materials are coated by a thin-film formation technique such as sputtering or vacuum evaporation. The non-magnetic material is provided to protect the magnetic films and is made of a material with an excellent wear-resistance, such as non-magnetic ferrite, ceramic or glass.
Moreover, the above metallic magnetic films can have a multi-layered construction, in which the magnetic films and the non-magnetic films are alternately laminated, as is well known in the art.
As has been described above, the magnetic head of the present invention can provide the following advantages. Since the magnetic core can be made of a magnetic material which has a high saturation magnetic flux density, a recording medium requiring high coercive forces can be recorded on adequately with a high density, and a narrow track head of any track width can be easily fabricated. Since the erasure widths can be changed as required for the recording track by controlling the thickness of the magnetic films of the erasure head, moreover, the recording density across the widthwise direction of the track can be increased. Since the pair of erasure heads are integrated, it is easy to fabricate a magnetic head which has a very precise effective recording track width. Since the recording and reproduction head and the erasure heads are easily integrated, furthermore, the magnetic head of the present invention can be mass-produced very easily.
Incidentally, details of the recording and playback head portion of the magnetic head of the present invention are disclosed in the specification entitled "Magnetic Head and Process of Fabrication Thereof", which was filed as a Japanese patent application No. 58-16067 on Feb. 4, 1983. The invention disclosed by the Japanese patent application No. 58-16067 is a copending application preceding the present invention but does not raises the prior art. Moreover, the Japanese patent application No. 58-16067 was also filed, claiming the convention priority, in the United States of America, Canada and Korea and before the European Patent Office (while designating England, West Germany, France and Netherlands).
The remaining portions of the magnetic head and its fabrication process according to the present invention, which are not described in the present specification, are within the technical knowledge in the prior art.